Engines may be automatically stopped and restarted automatically in the absence of an operator engine start request (e.g., an operator start request via a key or pushbutton) to conserve fuel. In one example, the engine may be stopped when predetermined conditions occur. For example, the engine may be stopped during a time when a vehicle brake pedal is depressed and when there is an absence of a driver requested engine torque. The engine may be restarted when predetermined conditions occur. For example, the engine may be restarted when the operator releases the brake pedal. However, if the engine is stopped and then restarted while a transmission of the vehicle is in a gear, the vehicle operator may experience a torque disturbance within the vehicle driveline (e.g., transmission, driveshaft, and vehicle wheels). The torque disturbance may be related to an amount of torque transmitted from the engine to the driveline via a torque converter. In particular, the torque converter may transmit torque from the engine to the vehicle driveline such that more engine torque is transmitted to the vehicle driveline at higher engine speeds.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for starting an engine, comprising: cranking the engine via a starter; and adjusting a spark timing for a cylinder of the engine to a timing retarded of top-dead-center compression stroke of the cylinder in response to a request to automatically start the engine, the spark timing for a first combustion event in the cylinder since a stop of the engine.
By providing spark to a cylinder of an engine at timing retarded of top-dead-center compression stroke it may be possible to start the engine while a transmission coupled to the engine is in drive such that the engine speed runs up to idle speed and driveline torque disturbances are reduced. In one example, spark timing is retarded such that average IMEP during a cylinder cycle is less than 4 bar. In this way, engine speed may be controlled such that the possibility of driveline torque disturbances may be reduced.
In another aspect of the present disclosure the inventors herein have provided a method for starting an engine, comprising: cranking the engine via a starter; in response to a controller requested engine start, adjusting spark timing of the engine to a first timing; and in response to an operator requested engine start, adjusting spark timing of the engine to a second timing, the second timing different than the first timing.
By providing different spark timings for controller initiated engine starts (e.g., engine starts in response to selected controller engine restart conditions being met and without an operator request to start the engine) and operator initiated engine starts (e.g., an engine restart responsive to an operator's request to restart an engine via a key-on or pushbutton input), it may be possible to limit an amount of engine torque transmitted to a vehicle driveline and provide enough torque to robustly start the engine.
For example, during a controller initiated engine start when the engine is warm, it may be desirable to provide spark at timing well in advance of MBT spark timing (e.g., minimum spark advance for best engine torque) so that less engine torque is provided by the engine as compared to when spark is provided to the engine at MBT spark timing. In this way, engine torque can be limited to control the amount of torque delivered to the vehicle driveline even when engine cylinders are full of air after an engine stop. On the other hand, it may be desirable to provide spark to the engine at a second timing when the engine is warm in response to an operator requested start when a transmission is in park.
In one example, spark provided to the engine may be retarded when an operator requests an engine start as compared to when a controller initiates an engine start. The spark timing during the operator initiated engine start may provide additional engine torque so that the engine accelerates at a higher rate and provides a stronger indication to the driver that the engine is started. In still other examples, higher torque may be provided during an operator initiated engine cold start to overcome engine friction at lower engine temperatures. Thus, it may be desirable to provide different spark timings to an engine depending on whether or not the engine start is requested by an operator.
The present description may provide several advantages. In particular, the approach may improve engine starting consistency. Further, the approach may provide improved engine emissions when a controller initiates an engine restart. For example, the engine may be restarted such that lower pressure combustion occurs during a controller initiated engine restart since lower pressure spark timing is adjusted away from MBT spark timing. Consequently, less NOx may be formed in engine cylinders during a controller initiated engine restart. Further, the approach may improve a driver's perception of vehicle starting when the engine is started automatically by reducing driveline torque disturbances.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.